The netboot set works on older machines.My first attempt to create the netboot set resulted in an error at creation that said my recovery partition version did not match my OS version. I fixed that in two different ways but neither resulted in a working netboot set:

Fix #1: http://www.deploystudio.com/Forums/viewtopic.php?id=7920Fix #2. I uploaded my AutoDMG generated 10.12.6 dmg to my deploystudio Masters. Then I netbooted the 2017 iMac to a machine-specific netboot set of 10.12.5 and restored 10.12.6 to the iMac.